“Microfossil fish teeth are perhaps the most abundant vertebrate fossils on the planet but can be really challenging to identify to specific taxonomic lineage — we can tell you a lot about the tooth but saying ‘this is the fish that made that tooth’ is not so simple,” said Elizabeth Sibert, a former Hutchinson Postdoctoral Fellow at the Yale institute of Biospheric Studies and senior author of the paper. “This study capitalized on a decade-long database project I’ve been developing which allowed us to positively identify some unique tooth features and make a confident taxonomic identification.”
The mineral composition of fish teeth prevents them from dissolving in the ocean’s corrosive bottom waters. A gram of ocean sediment can contain hundreds of fossilized teeth, which can be precisely dated using techniques for dating marine sediment cores, researchers said.
As with the teeth of extant species, most of the fossilized teeth the researchers studied were smooth. They did, however, find several examples of conical, curved teeth fossils from the Southern Ocean that bore spiraling striations indistinguishable from those on the teeth of living Cyclothone species. They determined that these fossils belonged to ancient Cyclothone or a Cyclothone-like stem lineage that lived at least 55 million years ago.
The discovery aligns the fossil record of Cyclothone with time-calibrated molecular phylogenies — evolutionary trees derived from genetic data — that estimate the genus’ origins to between 35 and 56 million years ago, the researchers explained.
The same method could be used to expand the fossil records of other groups of deep-sea fish with textured teeth, said Tennenbaum, a Marshall Scholar from Ann Arbor, Michigan, who will pursue a Doctor of Philosophy degree in biology at the University of Oxford beginning this fall.